In men and women over the age of 65, the skin blood flow (SkBF) in response to hyperthermia is severely attenuated. To date, we have elucidated the efferent neural pathway (the cutaneous active vasodilator system, a non-adrenergic efferent pathway unique to human skin) through which aging acts to decrease SkBF at a given core temperature (TC) and put this decreased SkBF within the context of overall cardiovascular regulation and blood flow distribution. We have also demonstrated that unopposed exogenous estrogen therapy (acute or chronic) increases the SkBF response to an elevated TC in postmenopausal women. We plan to systematically examine potential mechanisms through which these negative (aging) and positive (estrogen) effects are exerted using new approaches and technology. We plan to compare older and younger men and women to examine the mechanism by which aging attenuates reflex active cutaneous vasodillation.